For a multi-line click script, concatenate the lines together with a return in-between, as in the following example:

click script ("tell application \"Finder\"" & return & "open trash" & return & "end tell")

In AppleScript, the ampersand is used for string concatenation, and "return" is the carriage return character. Note also that embedded quotes are preceded by a backslash.

The iTunes Buttons example shows how to create a multi-line click script by concatenating the lines into a string variable, then using the variable for the click script.